I think if you took a poll of how many "true" friends each of us have the numbers would be quite small (0-3). These are the people that didn't disappear when life got tough, that like you even though they know the ugly stuff about you, and keep calling when you move 2000 miles away. These friends are the true diamonds and we each have a precious few.
Then there is everyone else. The ladies at work that you enjoy having lunch with, the people you can have over for a game night, or that you bbq with in the summer and all the kids have a great time. You have fun with these people, you don't have expectations of them being there for you, and if they turn up in times of hardship maybe they move into that inner circle of the precious few. Nobody starts in that inner circle, they grow there over time.
I think you need both kinds of friends in your life. I also think, as someone below mentioned, that to have true friends you have to be a true friend. But that doesn't mean you shouldn't have boundaries. If you find that your are visiting friends in the hospital, or crying with them through the hard times, to find yourself alone in your times of need, I don't think that is true friendship.
It was a hard lesson to learn for me to let go of the ones who take and take, but give nothing in return. I had one friend in particular I stayed a lot longer than I should have because of the "we have been through so much together thoughts." She was there for me through all of my happy times, even in the room when my daughter was born. When things got rough, I dropped everything and was there for her. Unfortunately, that was never reciprocated.
The answer to your question in short, is be yourself. Treat others the way you want to be treated. It won't always be reciprocated, but do it anyway. When it is reciprocated, you know you have a real friend.